It depends on the XP version that is used.
XP pro, 32 bit can handle 4 Gb, but XP pro 64 bit supports up to 128 Gb.
It also depends ofcourse on the hardware (chipset mainly).

80 Mb is only (around) 4% of 2 Gb.

On old(er) systems often speed can be increased by disabling not needed services, not letting applications start at boot time (and heaving them run in the background and such.
Also over time the systems get “polluted” with all kinds of things and a clean installation of the OS (and other things) almost always will bring a noticeable increase in speed.